1. Field of the Invention
The present invention relates to a screening apparatus used to screen acceptable and rejectable material from a fiber suspension, and, more particularly, relates to such a screening apparatus including a screen basket concentrically positioned relative to a rotor.
2. Description of the Related Art
In the paper-making process, a screening apparatus is typically used to separate foreign matter from a fiber suspension. A typical screening apparatus may include a housing within which a screen basket is mounted around a concentrically positioned rotor assembly. The screen basket may be fabricated from a relatively thin metal plate material although bar or wire materials are also often used and when mounted in a screening apparatus provide a barrier between a screening chamber and an accept chamber. The fiber suspension is transported into the screening chamber by way of a feed inlet. The fiber suspension is introduced to either the inner or outer portion of the screen basket, depending upon the particular type of screening apparatus being used. Material which does not pass through the screen basket flows to an end of the screening chamber away from the feed inlet and is removed through a reject outlet.
One known type of screen basket has circular shaped openings sized to reject unwanted solids and may have support rings located along the length of the basket to provide additional mechanical support. Another type of screen basket has slots having lengths much greater than their widths for separating other types of materials and may have support rings located along the length of the screen basket to provide additional mechanical support. Yet another type of screen basket includes longitudinally extending wires which are attached at each end thereof to respective annular retaining rings. The retaining rings are used to mount the screen basket within the screening apparatus. The retaining rings are bolted to a stationary member to prevent the screen basket from rotating in response to the torsional forces generated by the rotating hydrofoils or drum.
The rotor assembly generally includes hydrofoils or a contoured drum mounted on a rotating shaft in close proximity to the screen basket to sweep past the openings of the screen basket. The hydrofoils or contoured drum may be positioned to sweep over the inner or outer surface of the screen basket. The rotating hydrofoils or contoured drum generate hydrodynamic pulses in the radial direction with enough force and frequency to continuously remove any fiber plugs that occur in the screen basket openings. The localized flows caused by the hydrodynamic pulses are generally in a direction opposite to the flow of the fluid pulp provided to the screen basket under pressure.
With a screening apparatus as described above, flaking, defibering and screening occur almost entirely within the rotor as a result of hydrodynamic actions and pressure pulsations caused by the rotating foils within the rotor. Although such screening apparatus further result in effective screening of the fiber suspension, the rejects rate may be higher than desired because of insufficient deflaking and defibering.
What is needed in the art is a screening apparatus which provides improved deflaking, defibering and screening of the fiber suspension, thereby resulting in an increased accepts rate with lower power input requirements.
The present invention provides a screening apparatus including a rotor, a stationary defibering ring positioned above the rotor, and a rotor blade ring carried by the rotor and positioned above the stationary defibering ring.
The invention comprises, in one form thereof, a screening apparatus for screening acceptable and rejectable material from a pressurized fiber suspension, including a housing and a rotor within the housing. The rotor has a top end. A screen basket is positioned generally concentrically around the rotor. A rotor blade ring is connected to the top end of the rotor and rotates with the rotor. A stationary defibering ring is positioned adjacent to the rotor blade ring.
An advantage of the present invention is that improved deflaking, defibering and screening is provided.
Another advantage is that the rotor blade ring and/or stationary defibering ring may be selected with one of multiple different configurations while still providing improved functionality.